Optical displacement sensing system

ABSTRACT

An optical displacement sensing system is provided. With configuration of an optical sensor disposed on a displacement platform and in cooperation with a broadband light source and an optical spectrum analyzer, when the displacement platform moves, the waveguide grating of the optical sensor is resonated and the reflected light provided with a resonance wavelength is formed. The waveguide grating has the plurality of grating periods, and when the displacement platform moves to a different position to make the broadband light source correspond to a different grating period, the position can correspond to the different resonance wavelength. Therefore, according to the aforementioned configuration, the position is determined according to the different resonance wavelength, instead of using an optical encoder; furthermore, the micrometer-scale or nanometer-scale displacement detection is achieved.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional Application of co-pending applicationSer. No. 16/600,158, filed on Oct. 11, 2019, for which priority isclaimed under 35 U.S.C. § 120; this application claims the benefit ofTaiwan Patent Application No. 107135911, filed on Oct. 12, 2018, in theTaiwan Intellectual Property Office, under 35 U.S.C. § 119; thedisclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to an optical displacement sensing system,more particularly to an optical displacement sensing system which thereflected light with the resonance wavelength is generated when theincident light radiates on the waveguide grating during the movement ofthe displacement platform by means of the waveguide grating and thedisplacement platform.

2. Description of the Related Art

Conventional optical position sensing systems use a diffraction patternof a grating structure to detect displacement. Specifically, a lightsource emits the incident light to an optical encoder with the gratingstructure and the diffraction patterns are formed. Different diffractionpatterns are generated with the movement of the optical encoder. Theconventional optical position sensing system distinguishes positionsaccording to the difference between diffraction patterns. However, whenthe optical encoder suffers from the vibration, the diffraction patternswould change and the detection error of the position may be resulted.The conventional optical position sensing system requires high stabilityof the optical encoder.

U.S. Pat. No. 7,155,087B2 discloses a system using two parallel arraysconstituted of air holes to detect a change in displacement.Specifically, the incident light is incident on the two arrays andpasses through the two arrays to obtain an original light transmissionspectrum. When the distance between the two arrays is changed, theoriginal light transmission spectrum is changed to a varied lighttransmission spectrum, so that a displacement can be determinedaccording to the change between the original light transmission spectrumand the varied light transmission spectrum. However, the incident lightmust be coupled to the arrays constituted of air holes and the arraysare resonated, the polarization state of the incident light and theenvironmental for the incident light must be properly selected.Furthermore, the two arrays constituted of air holes also elongatelength of the displacement sensing system.

In order to solve above problems, the inventors of the present inventiondevelop an optical displacement sensing system.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide an opticaldisplacement sensing system, to solve the above-mentioned problems.

In order to achieve the objective, the present invention provides anoptical displacement sensing system comprising a broadband light source,a fiber collimator, an optical sensor, a displacement platform and anoptical spectrum analyzer. The broadband light source is configured toemit an incident light. The fiber collimator includes an input terminal,a sensing terminal and an output terminal; and the input terminal iscoupled to the broadband light source and configured to receive theincident light, and the sensing terminal is configured to transmit theincident light. The optical sensor is disposed adjacent to the sensingterminal and on a travelling path of the incident light, and configuredto receive the incident light. The optical sensor comprises a substrateand a waveguide grating. The waveguide grating includes a plurality ofgrating periods different from each other and disposed on the substrate.The waveguide grating is configured to be resonated by the receivedincident light, and to form a reflected light with a resonancewavelength and emitted to the sensing terminal. The displacementplatform is disposed adjacent to the optical sensor and on thetravelling path of the incident light. The displacement platform ismoved to a plurality of different positions corresponding to a pluralityof different grating periods, so that the plurality of differentpositions correspond to different ones of the resonance wavelength ofthe plurality of different rating periods. The optical spectrum analyzeris coupled to the output terminal to display a spectrum of the reflectedlight. By means of foregoing configuration, each position isdistinguishable based on the different resonance wavelength and there isno need for optical encoder and the incident light with specific phase.Besides, in the optical displacement sensing system of the presentinvention, the needed element is easy to obtain at low cost. The lengthof the present invention is shorter than that of the conventionaloptical position sensing system, and advantageously, the presentinvention is not sensitive to electromagnetic interferences.

Preferably, the substrate is located on a side away from the fibercollimator or close to the fiber collimator.

Preferably, the waveguide grating comprises a grating structure and awaveguide layer, the grating structure is disposed on the substrate, andthe waveguide layer is disposed on the grating structure.

Preferably, the waveguide grating includes a plurality of firstrefractive index regions and a plurality of second refractive indexregion alternately disposed thereon, and the refractive index of thefirst refractive index regions is higher than that of the secondrefractive index of the second refractive index regions.

Preferably, a displacement between the positions is in the micrometerscale.

Preferably, the optical displacement sensing system further comprises apolarizer disposed between the optical sensor and the sensing terminalto polarize the incident light.

Preferably, the plurality of grating periods comprises a maximal gratingperiod and a minimal grating period, a variation from the minimalgrating period to the maximal grating period is gradient.

Preferably, the displacement platform is moved based on a referencepoint which is a position corresponding to the minimal grating period.

In order to achieve the objective, the present invention provides anoptical displacement sensing system comprising an optical amplifier, afirst fiber collimator, a second fiber collimator, an incident mirror,an optical sensor, a reflector and a displacement platform. The opticalamplifier comprises an incident terminal, and a reflection terminal. Theincident terminal is configured to emit an incident light. The firstfiber collimator is coupled to the incident terminal, and the secondfiber collimator is coupled to the reflection terminal. The incidentmirror is disposed on a side of the first fiber collimator opposite tothe incident terminal, and configured to change a direction of theincident light. The optical sensor is disposed adjacent to the incidentmirror and on the travelling path of the incident light, and configuredto receive the incident light. The optical sensor comprises a substrateand a waveguide grating. The waveguide grating is provided with aplurality of grating periods different from each other and disposed onthe substrate. The waveguide grating is configured to receive theincident light and reflect a reflected light to the incident mirror, andthe incident mirror reflects the reflected light to the first fibercollimator. The reflector is disposed on a side of the second fibercollimator opposite to the reflection terminal, and configured toreceive the reflected light from the second fiber collimator, andreflect the reflected light to the second fiber collimator, so as toreflect the reflected light to the optical sensor. The reflected lightis travelled back and forth between the optical sensor and the reflectorto achieve a lasing condition for generating a laser beam. Thedisplacement platform is disposed adjacent to the optical sensor and onthe travelling path of the incident light. When the laser beam isincident on the incident mirror through the first fiber collimator, thelaser beam is then incident on the optical sensor to make the waveguidegrating of the optical sensor resonate, and the reflected laser beamwith a resonance wavelength is reflected from the waveguide grating. Thedisplacement platform is moved to the plurality of different positionscorresponding to a plurality of different grating period, so that theplurality of different positions correspond to different ones of theresonance wavelength of the plurality of different grating periods. Dueto the coherence of the laser beam and the plurality of the waveguidegrating with different grating periods, each different resonancewavelength corresponds to the different position, and the full width athalf maximum of each resonance wavelength is narrow. Therefore, eachposition is easy to distinguish.

Preferably, the substrate is located on a side away from or close to theincident mirror.

Preferably, the waveguide grating comprises a grating structure and awaveguide layer, the grating structure is disposed on the substrate, andthe waveguide layer is disposed on the grating structure.

Preferably, the waveguide grating comprises a plurality of firstrefractive index regions and a plurality of second refractive indexregions alternately disposed thereon, and the refractive index of thefirst refractive index regions is higher than that of the secondrefractive index of the second refractive index regions.

Preferably, a displacement between the positions is nanometer scale.

Preferably, the optical displacement sensing system further comprises abeam splitter and an optical spectrum analyzer. The beam splitter islocated between the reflector and the second fiber collimator, and thebeam splitter redirects the reflected laser beam to the optical spectrumanalyzer.

Preferably, the plurality of grating periods comprise a maximal gratingperiod and a minimal grating period, a variation from the minimalgrating period to the maximal grating period is gradient.

Preferably, the displacement platform is moved based on a referencepoint which is the position corresponding to the minimal grating period.

According to above-mentioned contents, the optical displacement sensingsystem of the present invention has at least one of the followingadvantages:

First, the optical displacement sensing system of the present inventioncan use the grating structure to obtain the reflected light with apreferred resonance wavelength, so as to distinguish different positionsaccording to different resonance wavelengths, instead of using anoptical encoder and the incident light with a specific phase, therebyachieving micrometer-scale or nanometer-scale displacement detection.

Secondly, the components of the optical displacement sensing system ofthe present invention can be obtained easily and at low-cost and theoptical displacement sensing system is insensitive to electromagneticinterferences.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operating principle and effects of the present inventionwill be described in detail by way of various embodiments which areillustrated in the accompanying drawings.

FIG. 1 is a configuration diagram of a first embodiment of an opticaldisplacement sensing system of the present invention.

FIG. 2 is a flow of manufacturing an optical sensor of a firstembodiment of an optical displacement sensing system of the presentinvention.

FIG. 3 is a structural diagram of an optical sensor of a firstembodiment of an optical displacement sensing system of the presentinvention.

FIG. 4 is a schematic diagram of configurations of an optical sensor ofa first embodiment of an optical displacement sensing system of thepresent invention.

FIG. 5 is an alternative structure diagram of a waveguide grating of afirst embodiment of an optical displacement sensing system of thepresent invention.

FIG. 6 shows curve diagrams of the light reflection spectrum andwavelength-versus-position of a first embodiment of an opticaldisplacement sensing system of the present invention.

FIG. 7 shows wavelength-versus-position curve diagrams of a firstembodiment of an optical displacement sensing system of the presentinvention.

FIG. 8 is a configuration diagram of a first embodiment of an opticaldisplacement sensing system using single wavelength, according to thepresent invention.

FIG. 9 is a configuration diagram of a first embodiment of an opticaldisplacement sensing system applied to measure an acceleration,according to the present invention.

FIG. 10 is a configuration diagram of a first embodiment of an opticaldisplacement sensing system applied to measure shear stress, accordingto the present invention.

FIG. 11 is a configuration diagram of a second embodiment of an opticaldisplacement sensing system of the present invention.

FIG. 12 shows curve diagrams of the light reflection spectrum andwavelength-versus-angle of a second embodiment of an opticaldisplacement sensing system of the present invention.

FIG. 13 shows curve diagrams of the light reflection spectrum andwavelength-versus-angle of a second embodiment of an opticaldisplacement sensing system of the present invention.

FIG. 14 is a configuration diagram of a second embodiment of an opticaldisplacement sensing system applied to sense torsion, according to thepresent invention.

FIG. 15 is a configuration diagram of a third embodiment of an opticaldisplacement sensing system of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following embodiments of the present invention are herein describedin detail with reference to the accompanying drawings. These drawingsshow specific examples of the embodiments of the present invention. Itis to be acknowledged that these embodiments are exemplaryimplementations and are not to be construed as limiting the scope of thepresent invention in any way. Further modifications to the disclosedembodiments, as well as other embodiments, are also included within thescope of the appended claims. These embodiments are provided so thatthis disclosure is thorough and complete, and fully conveys theinventive concept to those skilled in the art. Regarding the drawings,the relative proportions and ratios of elements in the drawings may beexaggerated or diminished in size for the sake of clarity andconvenience. Such arbitrary proportions are only illustrative and notlimiting in any way. The same reference numbers are used in the drawingsand description to refer to the same or like parts.

It is to be acknowledged that, although the terms ‘first’, ‘second’,‘third’, and so on, may be used herein to describe various elements,these elements should not be limited by these terms. These terms areused only for the purpose of distinguishing one component from anothercomponent. Thus, a first element discussed herein could be termed asecond element without altering the description of the presentdisclosure. As used herein, the term “or” includes any and allcombinations of one or more of the associated listed items.

It will be acknowledged that when an element or layer is referred to asbeing “on,” “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layer,or intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present.

In addition, unless explicitly described to the contrary, the word“comprise” and variations such as “comprises” or “comprising”, will beacknowledged to imply the inclusion of stated elements but not theexclusion of any other elements.

Please refer to FIG. 1, which is a configuration diagram of the firstembodiment of an optical displacement sensing system of the presentinvention. In this embodiment, the optical displacement sensing systemof the present invention includes a broadband light source 10, a fibercollimator 20, an optical sensor 30, a displacement platform 40 and anoptical spectrum analyzer 50. The broadband light source 10 emits anincident light. The fiber collimator 20 may be a 2×1 fiber module, andcomprise an input terminal 21, a sensing terminal 22, an output terminal23 and a collimator 24. The input terminal 21 is coupled to thebroadband light source 10 to receive the incident light, the collimator24 is disposed on the sensing terminal 22, and the sensing terminal 22transmits the incident light. The incident light passes through thecollimator 24 and travels toward the optical sensor 30. The opticalsensor 30 is disposed adjacent to the sensing terminal 22, and disposedon a travelling path of the incident light for receiving the incidentlight. The optical sensor 30 includes a substrate 31 and a waveguidegrating WG. The waveguide grating WG includes a waveguide layer 33 and agrating structure 32. The grating structure 32 has a plurality ofgrating periods P₁ to P_(n) different from each other and the gratingstructure 32 is disposed on the substrate 31. The waveguide layer 33 isdisposed on the grating structure 32. By receiving the incident light bythe waveguide grating WG, the waveguide grating WG is resonated by thereceived light to reflect the reflected light with a resonancewavelength to the sensing terminal 22. The displacement platform 40 isdisposed adjacent to the optical sensor 30 and on the travelling path ofthe incident light. The displacement platform 40 and the optical sensor30 are disposed perpendicular to the travel direction of the incidentlight. The displacement platform 40 is moved to a plurality of differentpositions corresponding to a plurality of different grating periods, sothat the plurality of different positions correspond to different onesof the resonance wavelength of the plurality of different gratingperiods. The optical spectrum analyzer 50 is coupled to the outputterminal 23 to display the spectrum of the reflected light, so that auser can know the resonance wavelength of the reflected light. Accordingto the aforementioned configuration, the position can be distinguishedaccording to different resonance wavelengths, instead of using anoptical encoder and the incident light with a specific phase;furthermore, the optical displacement sensing system of the presentinvention can sense the micrometer-scale displacement between thepositions. Moreover, the components of the optical displacement sensingsystem of the present invention can be obtained easily at low-cost, andthe system size of the optical displacement sensing system of thepresent invention is smaller than that of the conventional opticaldisplacement sensing system. The optical displacement sensing system ofthe present invention has the advantage of not being sensitive toelectromagnetic interferences.

It should be noted that the optical displacement sensing system of thepresent invention can be applied to a mobile object or device, and it isnot necessary to use the displacement platform 40 to assist movement fordetection. The displacement platform 40 is merely used to assist themovement of the optical sensor 30, for example, the optical sensor 30can be disposed on a displacement device with a micrometer scale chipand in cooperation with the components of the optical displacementsensing system of the present invention instead of the displacementplatform 40, so as to accurately measure the displacement of the chip.

It should be noted that the optical displacement sensing system of thepresent invention can perform the resonance of the waveguide grating bythe guided-mode resonance principle, and the waveguide grating isconstituted of the grating structure and the waveguide. In detail, theconfiguration of the materials and the grating period of the grating,and the thickness and the number of layers of the waveguide gratingallow the incident light with a specific wavelength to be coupled intothe waveguide through phase matching provided by the grating structure.Due to the reciprocity, the in-coupled light will be coupled out to intograting structure direction to form the multiple reflected light andinto substrate direction to form the multiple transmitted light. Themultiple reflected lights create constructive interference withzero-order backward-diffracted light, so that the reflectivity of thereflected light with the specific wavelength is close to 100%, and themultiple transmitted light and the zero-order forward-diffracted lightform destructive interference, so that the transmittance of thetransmitted light at a specific wavelength is close to zero. Due to theexistence of the above phenomenon, an optical filter may be fabricatedusing this guided-mode resonance principle.

Specifically, a plurality of grating periods P₁ to P_(n) different fromeach other include a maximal grating period P_(n) and a minimal gratingperiod P₁, the variation from the minimal grating period P₁ to themaximal grating period P_(n) is gradient; for example, the maximalgrating period P_(n) can be 550 nm, the minimal grating period P₁ can be250 nm, and the gradient variation from the minimal grating period P₁ tothe maximal grating period P_(n) is 2 nm, and the gradient variation canalso be adjusted according to design requirements of the gratingstructure 32, and the scope of the present invention is not limited toabove example. The displacement platform 40 is moved based on areference point which is the position corresponding to the minimalgrating period P₁. Since the grating structure 32 has various gratingperiods P₁ to P_(n), the displacement platform 40 is able to correspondto different grating period while moving, so as to change the resonancewavelength of the reflected light. As a result, compared with thecomponent configuration of the conventional optical displacement sensingsystem, the optical displacement sensing system of the present inventionis simplified and can use the position corresponding to other gratingperiod as the reference point according to the displacement requirement,and the scope of the present invention is not limited to above example.

Furthermore, the optical displacement sensing system of the presentinvention includes a polarizer 60 disposed between the optical sensor 30and the sensing terminal 22, and configured to polarize the incidentlight; preferably, the incident light can be the light in TE mode or TMmode, so that the resonance wavelength generated by the incident lightin the TE mode or TM mode can be measured.

It is worth noting that the fiber collimator 20 can be a 2×2 fibermodule which has more sensing terminal 22 than the 2×1 fiber module. Inthis embodiment, the fiber collimator 20 comprises two sensing terminals22, one of the two sensing terminal 22 is a port for emitting incidentlight, and the other is a port for receiving the reflected light, sothat the incident angle of the incident light can be adjusted, toachieve the purpose that the incident light is obliquely incident on theoptical sensor 30 and the reflected light is obliquely reflected to thefiber collimator 20. When the optical sensor 30 is at an obliqueposition, the displacement measurement can be performed through the 2×2fiber collimator 20.

Please refer to FIGS. 2 and 3, which are flow of manufacturing theoptical sensor of the first embodiment of the optical displacementsensing system of the present invention and a structural diagram of anoptical sensor of the first embodiment of the optical displacementsensing system of the present invention, respectively. As shown in FIGS.2 and 3, the substrate 31 is a PET substrate, the grating structure 32is formed by Norland 68, which is Norland Optical Adhesive 68, and thewaveguide layer 33 is formed by TiO₂. The flow of manufacturing processof the optical sensor 30 is described as follows. First, Norland68 isapplied to the silicon mold which has a structure corresponding to thegrating structure 32. Secondly, the PET substrate is disposed on theNorland 68, and the Norland 68 is irradiated with ultraviolet light, soas to cure the Norland68 to form the grating structure 32. Thirdly, themold turning process is performed to separate the PET substrate havingthe Norland 68 from the silicon mold. Finally, a TiO₂ layer is depositedon the Norland 68 to form a waveguide layer 33, thereby completelyforming the optical sensor 30 as shown in FIG. 3. Preferably, the methodof depositing the TiO2 layer can include sputtering method, chemicalvapor deposition method, pulsed laser deposition method, or molecularbeam epitaxy method, and so on, but the scope of the present inventionis not limited thereto.

It should be noted that the grating structure 32 can also be formed byfirst depositing a semiconductor layer, and then performing wet etchingor dry etching on the semiconductor layer; however, the scope of thepresent invention is not limited to above example. The range of theresonance wavelength of the grating structure 32 can be determinedaccording to the grating periods, the material and thickness of thewaveguide grating, and the range of the wavelength band of the lightsource is also determined accordingly. Therefore, the wavelength rangesof the resonance wavelength and the broadband light source 10 are notlimited in the present invention.

Please refer to FIG. 4, which is a schematic diagram of configurationsof an optical sensor of a first embodiment of an optical displacementsensing system of the present invention. As shown in FIG. 4, theincident light can be incident on the substrate 31 and then radiated onthe waveguide grating WG to generate the reflected light with theresonance wavelength, and the substrate 31 is located on the side closeto the fiber collimator 20; alternatively, the incident light can beincident on the waveguide grating WG and then radiated on the substrate31 to generate the reflected light with the resonance wavelength, andthe substrate is located on the side away from the fiber collimator 20.The aforementioned two configurations can generate the reflected lightwith the resonance wavelength, thereby achieving the purpose of sensingdisplacement.

Please refer to FIG. 5, which is an alternative structural diagram ofthe waveguide grating of the first embodiment of the opticaldisplacement sensing system of the present invention. As shown in FIG.5, the waveguide grating WG is in a single-layer structure and formed bya plurality of first refractive index regions HR and a plurality ofsecond refractive index regions LR disposed alternately. The refractiveindex of the first refractive index regions is higher than that of thesecond refractive index of the second refractive index regions. Thesingle first refractive index HR and the single second refractive indexregion LR can form a grating period. The thicknesses, the material andthe period of each first refractive index region HR and each secondrefractive index region LR may be adjusted according to the requirementin the resonance wavelength, so that the waveguide grating WG may havemultiple grating periods P₁ to P_(n) different from each other and isable to reflect the reflected light with the resonance wavelength;furthermore, the numbers of the first refractive index region HR and thesecond refractive index region LR may be adjusted according to therequirement in displacement amount; however, the scope of the presentinvention is not limited to above examples. The material of the firstrefractive index region HR may include tantalum pentoxide (Ta₂O₅),niobium pentoxide (Nb₂O₅), titanium dioxide (TiO₂), zirconium dioxide(ZrO₂), hafnium oxide (HfO₂) and oxidation Zinc (ZnO); and the materialof the second refractive index region LR may include magnesium fluoride(MgF₂), cerium oxide (SiO₂), calcium fluoride (CaF₂), barium fluoride(BaF₂) and aluminum oxide (Al₂O₃).

Please refer to FIG. 6, which show curve diagrams of reflected lightspectrum and wavelength-versus-position of the first embodiment of theoptical displacement sensing system of the present invention. As shownin the part (a) of FIG. 6, the displacement platform 40 starts from thereference point at 0 mm and moves by 0.5 mm, a position is set every 0.5mm, that is, the displacement is 0.5 mm, and the position at 6 mm is setas the last movement point. Since each position corresponds to differentgrating period, each position corresponds to the different period, andthe wavelengths with the highest reflectivity of each positions aredifferent from each other that is, the resonance wavelengths of thepositions are not the same. The resonance wavelengths of all positionsare shown in the part (b) of FIG. 6. The resonance wavelengths are notlinear with the displacements, but the relationship between theresonance wavelength and the displacement can be linearly fitted as astraight line of y=67.315x+455.72, wherein y is the resonance wavelengthand x is the position, and a slope value of the straight line is thesensitivity, and it can be found that an average sensitivity of theoptical displacement sensing system of the present invention is 67.315nm/mm.

Please refer to FIG. 7, which shows wavelength-versus-position diagramsof the first embodiment of the optical displacement sensing system ofthe present invention. In the parts (a), (b), and (c) of FIG. 7, thepositions at 1 mm, 3 mm and 5 mm are set as the reference points,respectively, and displacement is 0.05 mm. The linear fitting operationis also performed on the data, it can be found that the sensitivity is80.2 nm/mm, 59.5 nm/mm and 56.8 nm/mm in the parts (a), (b), and (c) ofFIG. 7, respectively. In summary, the grating period corresponding tothe position at 1 mm is less than the grating period corresponding tograting period of the position at 5 mm, so that the sensitivitycorresponding to the position at 1 mm is higher than the sensitivitycorresponding to the position at 5 mm.

Please refer to FIG. 8, which is the first embodiment of the opticaldisplacement sensing system of the present invention using a lightsource of single wavelength. As shown in FIG. 8, the incident light hasa single wavelength of 600 nm, and is incident on the position of thedisplacement platform 40 corresponding to the resonance wavelength of600 nm through the sensing terminal 22 and the position of thedisplacement platform 40 corresponding to the resonance wavelength of620 nm, respectively. The grating period corresponding to the resonancewavelength of 600 nm is different from the grating period correspondingto the resonance wavelength of 620 nm, so that the resonance effect ofthe grating period corresponding to the resonance wavelength of 600 nmis different from the resonance effect of the grating periodcorresponding to resonance wavelength of 620 nm. The light intensity ofthe position corresponding to the resonance wavelength of 600 nm isincreased because the wavelength of the incident light matches theresonance wavelength of this position, and the light intensity of theposition corresponding to the resonance wavelength of 620 nm isdecreased because the wavelength of the incident light is different fromthat of this position. According to the above description, the resonanceeffect of the single-wavelength light may increase at the positioncorresponding to the resonance wavelength the same as that of thesingle-wavelength light, so that the intensity of such positioncorresponding to the resonance wavelength is enhanced; the resonanceeffect of the single-wavelength light may be decreased at the positionalpoint not corresponding to the resonance wavelength, so that the lightintensity of such position is weakened, thereby understanding that thelight intensity is correlated with the displacement distance. Therefore,the light with the single wavelength may be utilized and the positioncorresponding to the single-wavelength light may be set as the referencepoint, and the displacement between the reference point and otherposition may be determined according to the light intensity.

Please refer to FIG. 9, which is a configuration diagram of the firstembodiment of the optical displacement sensing system of the presentinvention applied to measure acceleration. As shown in FIG. 9, when thedisplacement platform 40 accelerates, the optical sensor 30, which issuspended by auxiliary rods, can be moved on a direction opposite to theacceleration direction of the displacement platform 40 due to inertiaprinciple. The incident light is incident on different grating periodsof the waveguide grating 40 before and after acceleration of thedisplacement platform 40, respectively, so that the resonancewavelengths of the incident light are different before and afteracceleration of the displacement platform 40, respectively, and thedisplacement can be determined according to the difference of resonancewavelength, and the acceleration can be estimated according to thedisplacement and a time difference.

Please refer to FIG. 10, which is a configuration diagram of a firstembodiment of the optical displacement sensing system applied to measureshear stress, according to the present invention. As shown in FIG. 10,the optical sensor 30 is set at the hollow part of the displacementplatform 40, the optical sensor 30 is suspended by auxiliary rods. Whenthe displacement platform 40 is subjected to the shear stress, theoptical sensor 30 can be moved, and the incident light is incident ondifferent grating periods of the waveguide grating WG before and afterthe displacement platform 40 is subjected to the shear stress, and itcauses different resonance wavelengths of incident light before andafter the displacement platform 40 is subjected to the shear stress, sothat the displacement can be obtained according to the difference in theresonance wavelengths, and a value of the shear stress can be obtainedaccording to a shear stress formula and the displacement.

Please refer to FIG. 11, which is a configuration diagram of a secondembodiment of optical displacement sensing system of the presentinvention. As shown in FIG. 11, the difference between the secondembodiment and the first embodiment is in the displacement platform 40,which is a rotary displacement platform in the second embodiment, andthe configuration of the transducer 70 and the controller 80. The othercomponents of the second embodiment are the same as that of the firstembodiment, so the detailed descriptions are not repeated herein. Indetail, the optical sensor 30 is disposed on a cylinder, and thecylinder with the optical sensor 30 is connected to a rotary disc, andthe transducer 70 is set below the rotary disc. The transducer 70 andthe controller 80 are electrically connected to each other, andconfigured to rotate the displacement platform 40.

When the controller 80 sends a control command to the transducer 70, thetransducer 70 rotates the displacement platform 40 according to thecontrol command, and the grating period of the waveguide grating WG onwhich the incident light is incident is also changed, so that theposition of the resonance wavelength is changed according to thedifferent grating periods of the waveguide grating WG.

Furthermore, the optical displacement sensing system of the presentinvention can be applied to a rotary object, and it does not necessarilyrequire the transducer 70, the controller 80 and the displacementplatform 40 to assist rotation of the optical sensor 30 for detection;the transducer 70, the controller 80 and the displacement platform 40are used to only assist the rotation of the optical sensor 30. Forexample, the optical displacement sensing system of the presentinvention can be applied to a motor, and the motor can be in cooperationwith the components of the optical displacement sensing system of thepresent invention instead of the displacement platform 40, so that arotation angle and an operational state of the motor can be accuratelymeasured.

Please refer to FIG. 12, which shows curve diagrams of reflected lightspectrum and wavelength-versus-position of a second embodiment of anoptical displacement sensing system of the present invention. As shownin the part (a) of FIG. 12, the displacement platform 40 starts from thereference point at 0 degrees and is moved by 0.5 degrees, a position isset every 0.5 degrees, that is, the displacement is 0.5 degrees, and thefinal movement position is set at 7 degrees. Each position correspondsto different grating period, and it causes that the wavelength of thehighest reflectivity corresponding to each position is different, sothat the resonance wavelengths of all positions are different from eachother, and resonance wavelengths of all positions are shown in part (b)of FIG. 12. The resonance wavelengths are not linear with thedisplacements, but the relationship between the resonance wavelength andthe displacement can be linearly fitted as a straight line:y=51.677x+434.24, wherein y is resonance wavelength and x is theposition, and a slope value of the straight line is a sensitivity, andan average sensitivity of the second embodiment of the opticaldisplacement sensing system of the present invention is 51.677nm/degree.

Please refer to FIG. 13, which show curve diagrams of reflected lightspectrum and wavelength-versus-position of the second embodiment of theoptical displacement sensing system of the present invention. As shownin part (a) of FIG. 13, the reflectance curve at positional point with0.5 degrees can be fitted, through an appropriate curve (e.g. Gaussian)of the computer, as a smoothed reflectivity curve. As shown in part (b)of FIG. 13, the position at 0.5 degree is set as a starting point, andthe displacement is 0.005 degrees, and five smooth reflectance curvescan be fitted by using the Gaussian curve of the computer.

As shown in the parts (c), (d), and (e) of FIG. 13, the positions at 0.5degrees, 3.5 degrees, and 6.5 degrees are set as reference points,respectively, and the displacement is 0.005 degrees, the linear fittingis also performed to obtain the sensitivities of 57 nm/degree, 41.8nm/degree and 27.5 nm/degree, respectively. In summary, the gratingperiod corresponding to the position of 0.5 degrees is less than thegrating period corresponding to the position of 6.5 degrees, so that thesensitivity corresponding to the position of 0.5 degree is higher thanthe sensitivity of the position of 6.5 degrees.

Please refer to FIG. 14, which is a configuration diagram of a secondembodiment of the optical displacement sensing system applied to sense atorsion force, according to the present invention. As shown in FIG. 14,when a torsion force is applied to a torsion shaft, the displacementplatform 40 is rotated and the optical sensor 30 disposed on thedisplacement platform 40 is also rotated, so that the grating periods ofthe waveguide grating on which the incident light is incident aredifferent before and after the displacement platform 40 is subjected tothe torsion force, respectively. Therefore, the resonance wavelengthbefore the displacement platform 40 subjected to the torsion isdifferent from the resonance wavelength after the displacement platform40 is subjected to the torsion, and the displacement can be obtainedaccording to the difference of the resonance wavelengths, and the valueof the torsion can be obtained according to a torsional formula and thedisplacement.

Please refer to FIG. 15, which is a configuration diagram of a thirdembodiment of an optical displacement sensing system of the presentinvention. In the third embodiment, the optical displacement sensingsystem of the present invention includes an optical amplifier 100, afirst fiber collimator 200, a second fiber collimator 300, an incidentmirror 400, an optical sensor 500, a reflector 600 and a displacementplatform 700. The optical amplifier 100 may be a semiconductor opticalamplifier and include an incident terminal 101 and a reflection terminal102, and the incident light is emitted from the incident terminal 101.The first fiber collimator 200 may include a single mode fiber and afirst collimator 201, the first collimator 201 is coupled to theincident terminal 101 through the single mode fiber. The second fibercollimator 300 can include a single mode fiber and a second collimator301, and the second collimator 301 is coupled to the reflection terminal102 through the single mode fiber. The incident mirror 400 is disposedon a side of first fiber collimator 200 opposite to the incidentterminal 101, and configured to change the direction of the incidentlight. The optical sensor 500 is disposed adjacent to the incidentmirror 400 and disposed on the travelling path of the incident light toreceive the incident light. The optical sensor 500 includes a substrate501 and a waveguide grating WG. The waveguide grating WG comprises awaveguide layer 503 and a grating structure 502. The grating structure502 has a plurality of grating periods P₁ to P_(n) different from eachother, and is disposed on the substrate 501. The waveguide layer 503 isdisposed on the grating structure 502. By receiving the incident lightby the waveguide grating WG, the waveguide grating WG can reflect areflected light to the incident mirror 400, and the incident mirror 400reflects the reflected light to the first fiber collimator 200. Thereflector 600 is disposed on a side of the second fiber collimator 300opposite to reflection terminal 102, and configured to receive thereflected light from the second fiber collimator 300 and reflect thereflected light back to the second fiber collimator 300, so that thereflected light can enter the optical sensor 500. As result, thereflected light can travel back and forth between the optical sensor 500and the reflector 600 to achieve the laser condition, so as to generatea laser beam. The displacement platform 700 is disposed adjacent to theoptical sensor 500 and on the travelling path of incident light. Whenthe laser beam is incident on the incident mirror 400 through the firstfiber collimator 200, the laser beam is incident on the optical sensor500, and the grating structure 502 of the optical sensor 500 isresonated by the laser beam and reflects the reflected laser beam withthe resonance wavelength. Hence, when the displacement platform 700 ismoved to a plurality of different positions corresponding to a pluralityof different grating periods, the plurality of different positionscorrespond to different ones of the resonance wavelength of theplurality of different grating periods. Since the coherence of the laserbeam and the configuration of the grating structure 502 with themultiple grating periods, each of the plurality of different resonancewavelengths correspond to a plurality of different positionsrespectively, and the full width half maximum of each resonancewavelength is quite narrow, so that each position may be distinguishedvery easily, and the nanometer-scale displacement between positions canbe sensed.

It should be noted that the optical sensor 500 and the reflector 600 canform a resonant cavity, and the reflected light is reflected back andforth in the resonant cavity. At the same time, the resonance wavelengthoccurs when the reflected light enters the grating structure 502, andwith the current control of the optical amplifier 100, the intensity ofthe resonance wavelength of the reflected light can be enhanced and thefull width half maximum of the reflected light can be narrowed. When thereflected light achieves the lasing condition that the optical gain isgreater than the loss, the laser beam with a very narrow full width halfmaximum is formed.

It should be noted that the optical sensor 500 of the third embodimentis the same as the optical sensor 30 of the first embodiment, theplurality of different grating periods P₁ to P_(n) include a maximalgrating period P_(n) and a minimal grating period P₁, the variation fromthe minimal grating period P₁ to the maximal grating period P_(n) isgradient, for example, the maximal grating period P_(n) may be 550 nm,the minimal grating period P₁ may be 250 nm, the variation gradient fromthe minimal grating period P1 to the maximal grating period P_(n) may be2 nm, and the gradient variation may be adjusted according to the designrequirements of grating structure 502, and the scope of the presentinvention is not limited to above example. The displacement platform 700is moved based on a reference point which is the position correspondingto the minimal grating period P1, and since the grating structure 502has various grating periods P₁ to P_(n), the displacement platform 700can correspond to different grating period while moving, so as to makethe resonance wavelength of the reflected light vary. Compared with thecomponent configuration of the conventional optical displacement sensingsystem, the component configuration of the optical displacement sensingsystem of the present invention is more simple, and other the positioncorresponding to other grating period may be used as the reference pointaccording to displacement requirement, and the scope of the presentinvention is not limited to above example.

Furthermore, the optical displacement sensing system of the presentinvention may include a beam splitter 800 and an optical spectrumanalyzer 900. The beam splitter 800 is located between the reflector 600and the second fiber collimator 300, and configured to split a laserbeam, and the beam splitter 800 can make the reflected laser beam emitto the optical spectrum analyzer 900, so that the spectrum of thereflected laser beam can be observed.

It is worth noting that with the resonant cavity formed by the opticalsensor 500 and the reflector 600 and the current control scheme of theoptical amplifier 100, the intensity of the resonance wavelength ofreflected laser beam can be enhanced and the full width half maximum ofthe reflected laser beam can be narrowed, so that the laser beam with ahigh quality factor can be formed, thereby improving a standarddeviation of the resonance wavelength and achieving the goal of sensingthe nanometer-scale displacement.

Similarly, the incident light can be first incident on the substrate 501and then radiated on the waveguide grating WG, to generate the reflectedlight with the resonance wavelength, and the substrate 501 is located onthe side close to the reflector 600; alternatively, the incident lightcan also be first incident on the waveguide grating WG and then radiatedon the substrate 501, to generate the reflected light with the resonancewavelength, and the substrate 501 is located a side away from thereflector 600. The aforementioned two configurations can generate thereflected light with the resonance wavelength, to achieve the purpose ofsensing displacement.

Furthermore, in the embodiment, the waveguide grating WG can also be asingle-layer structure, as shown in FIG. 5, and include a plurality offirst refractive index regions HR and a plurality of second refractiveindex regions LR alternately disposed thereon, and single firstrefractive index HR and single second refractive index region LR canform a grating period, and the thicknesses and materials of each firstrefractive index region HR and each second refractive index region LR,and grating period can be adjusted according to the requirement in theresonance wavelength. Hereby, the waveguide grating WG have multiplegrating periods P₁ to P_(n) different from each other, and can reflectthe reflected light with the resonance wavelength. The numbers of thefirst refractive index regions HR and the second refractive indexregions LR can be adjusted according to the requirement in displacement,but the scope of the present invention is not limited to above example.Since the materials of the first refractive index region HR and thesecond refractive index region LR are described in the first embodiment,so the descriptions are not repeated herein.

According to above contents, the optical displacement sensing system ofthe present invention can use the configuration of the grating structure32 having multiple grating periods P₁ to P_(n) different from eachother, to make the displacement platform 40 correspond to differentgrating period while displacement platform 40 is moving, and theresonance wavelengths of the positions are different from each other, sothat the displacement can be determined according to the differencebetween resonance wavelengths, instead of using the optical encoder andthe incident light with the specific phase, thereby achieving thepurpose of micrometer-scale displacement detection. Furthermore, theoptical displacement sensing system of the present invention can beapplied to detect angle, acceleration, shear stress and torsion. Insummary, the optical displacement sensing system of the presentinvention can have the advantages as described above, and the requiredcomponents are easy to obtain and low cost, and the optical displacementsensing system of the present invention can achieve micron-scaledisplacement detection, and even nano-scale displacement detection.

The present invention disclosed herein has been described by means ofspecific embodiments. However, numerous modifications, variations andenhancements can be made thereto by those skilled in the art withoutdeparting from the spirit and scope of the disclosure set forth in theclaims.

What is claimed is:
 1. An optical displacement sensing system,comprising: a broadband light source configured to emit an incidentlight; a fiber collimator comprising an input terminal, a sensingterminal and an output terminal, the input terminal being coupled to thebroadband light source and configured to receive the incident light, andthe sensing terminal being configured to transmit the incident light; anoptical sensor disposed adjacent to the sensing terminal and on atravelling path of the incident light, and configured to receive theincident light, the optical sensor comprising: a substrate; and awaveguide grating with a plurality of grating periods different fromeach other and disposed on the substrate, the waveguide grating beingconfigured to be resonated by the received incident light and to form areflected light with a resonance wavelength and emitted to the sensingterminal, wherein the plurality of grating periods comprises a maximalgrating period and a minimal grating period, a variation from theminimal grating period to the maximal grating period is gradient; adisplacement platform disposed adjacent to the optical sensor and on thetravelling path of the incident light, the displacement platform beingmoved to a plurality of different positions corresponding to a pluralityof different grating periods, so that the plurality of differentpositions correspond to different ones of the resonance wavelength ofthe plurality of different grating periods; and an optical spectrumanalyzer coupled to the output terminal to display a spectrum of thereflected light.
 2. The optical displacement sensing system according toclaim 1, wherein the substrate is located on a side away from the fibercollimator or close to the fiber collimator.
 3. The optical displacementsensing system according to claim 1, wherein the waveguide gratingcomprises a grating structure and a waveguide layer, the gratingstructure is disposed on the substrate, and the waveguide layer isdisposed on the grating structure.
 4. The optical displacement sensingsystem according to claim 1, wherein the waveguide grating includes aplurality of first refractive index regions and a plurality of secondrefractive index region alternately disposed thereon, with the firstrefractive index regions having a refractive index higher than that ofthe second refractive index regions.
 5. The optical displacement sensingsystem according to claim 1, wherein a displacement between thepositions is in a micrometer scale.
 6. The optical displacement sensingsystem according to claim 1, further comprising a polarizer disposedbetween the optical sensor and the sensing terminal.
 7. The opticaldisplacement sensing system according to claim 1, wherein thedisplacement platform is moved based on a reference point which is aposition corresponding to the minimal grating period.